A. Technical Field
The present invention relates to a pestivirus vaccine, which is capable of reducing clinical signs of congenital tremor (CT) or myoclonia congenita. The condition is informally known as shaking piglets, shaker piglets, or trembling piglets.
Pestivirus is a genus of viruses, in the family Flaviviridae. Viruses in the genus Pestivirus infect mammals, including members of the family Suidae (which includes various species of swine).
CT is a sporadic disease seen in newborn pigs. Usually more than one pig is affected in a litter. If the tremors are too great for the piglets to find a teat and suckle then mortality may be high. Mortality in an affected litter or in a herd outbreak could increase above the norm by 3-10%. The condition decreases as the affected piglets grow.
CT is classified into five types. Types AI, AIII, MV and AV are related to exposure to classical swine fever virus, genetic traits, or exposure to trichlorfon. As these causes are known and therefore avoided, type AII, is hypothesized to be the most common cause. Type AII is thought to be associated with a viral infection. The causal virus in group 2, is widespread among most if not all pig populations, yet little disease is seen in most herds, presumably because an immunity is established in the sow herd. In new gilt herds however, there can be major outbreaks involving up to 80% of all litters during the first parity. This is an unquantifiable risk in any new gilt herd.
The reason that pigs are born trembling is secondary to the primary lesion of hypomyelination or demyelination of the brain and spinal cord. There is no specific treatment for this condition. However, assisted suckling and provision of an environment where chilling and overlaying can be avoided will allow more pigs to recover with time, although weaning weights may be depressed by 1 kg or more.
B. Description of the Related Art
While there were early reports that porcine circovirus type 1 and type 2 infections (See, Burnborg et al., “Association of myocarditis with high viral load of porcine circovirus type 2 in several tissues in cases of fetal death and high mortality in piglets. A case study.” J Vet Diagn Invest. 19(4):368-375, 2007), or astrovirus (See Blomstrom et al., “Astrovirus as a possible cause of congenital tremor type AII in piglets?” Acta Vet Scand. 56(1):82, 2014) were the cause of CT, this has since been disproved (See Ha et al., “Lack of evidence of porcine circovirus type 1 and type 2 infection in piglets with congenital tremors in Korea”, Vet Rec. (2005) 156:383-384; Kennedy et al., “Absence of evidence of porcine circovirus infection in piglets with congenital tremors” J Vet Diagn Invest. 2003 March; 15(2):151-156). Thus, there is no clear pathogenic source of type AII CT in piglets and therefore, no effective treatment of this condition.